Thermal inkjet printheads eject fluid ink drops from nozzles by passing electrical current through resistor elements contained in a firing chamber. Heat from a resistor element creates a rapidly expanding vapor bubble that forces a small ink drop out of a nozzle of the firing chamber. When the resistor element cools, the vapor bubble quickly collapses and draws more fluid ink into the firing chamber in preparation for ejecting another drop through the nozzle. Fluid ink is drawn from a reservoir via a fluid slot that extends through the substrate on which the resistor element and the firing chamber are formed.